The invention relates to a method for detecting living human skin.
Modern access authorization systems may, inter alia, use fingerprints for identification purposes. An essential precondition for such an identification is that it must be protected against forgery or manipulation. In particular, it must be ensured that it is not possible to obtain access authorization with fake fingers or cut-off fingers. It is therefore essential also to check, together with the fingerprint, that the person with this fingerprint is alive.
Various methods for an electronic identification of persons are described in International Publication No. WO 95/26013. In addition to recording a fingerprint, these methods can determine whether the person is alive. These methods include recording the pulse frequency or electrocardiographic signals, measuring the oxygen content of the blood, the skin temperature, the blood pressure or mechanical properties of the skin surface.
It is accordingly an object of the invention to provide a method for detecting living human skin which is simple and which is suitable, in particular, for use in conjunction with a fingerprint sensor.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for detecting living human skin, the method includes the steps of:
providing a region of a skin surface close to at least one electric conductor by bringing the region of the skin surface in contact with the at least one electric conductor or by providing the region of the skin surface at a given distance from the at least one electric conductor;
applying an electric potential of a superimposition of frequencies or an electric AC voltage with a variable frequency to the at least one electric conductor;
determining, with a measurement carried out with the electric potential or the electric AC voltage, an electric impedance as a specific function of time and/or frequency, by determining a real part and an imaginary part of the electric impedance or by determining a frequency and an absolute value of the electric impedance; and
checking whether the specific function corresponds to a reference function.
According to another mode of the invention, the electric potential is provided as a superimposition of frequencies, wherein the superimposition results in a voltage pulse or a voltage jump.
According to yet another mode of the invention, the electric potential is provided by superimposing the frequencies of a limited interval.
According to a further mode of the invention, the region of the skin surface is provided close to at least two electric conductors by bringing the region of the skin surface in contact with the at least two electric conductors or by providing the region of the skin surface at a given distance from the at least two electric conductors. The at least two electric conductors are electrically insulated from one another and are spaced by a distance of at least 2 mm from one another.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for detecting living human skin, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.